The kidney plays a major role in the regulation of blood pressure in part by controlling extracellular volume. The renal dopaminergic system is involved in regulating sodium and water balance. This protocol investigates whether the renal-specific prodrug, gludopa, when administered in doses to produces physiologic concentrations of DOPA and dopamine, will alter dopamine production in a dose-dependent fashion in humans. Have not begun this study due to need for approval of gludopa for human administration.